Conventional gas furnaces are known to have an efficiency on the order of 65 percent. However, such furnaces are in disfavor with society and governmental agencies because they are inconsistent with present day efforts to avert a fuel shortage and to practice conservation.
Conventional furnaces have given way to mid efficiency and high efficiency furnaces, the former having an efficiency range on the order of 80 percent, and the latter having an efficiency rating above 90 percent. Typically, efficiency of modern furnaces has been increased by aggravating the complexity of the heat exchangers, providing circuitous paths for air to flow through the heat exchangers to receive heat from the burners therebelow. In like manner, the combustion chamber of the furnace is also of a circuitous nature, greatly resticting the actual draft from the combustion chamber to the flue or associated chimney. Indeed, it has been found that blowers must be employed with the combustion chambers of high efficiency furnaces in order to induce sufficient draft to maintain the requisite combustion. In other words, a draft assist, in the form of a blower or the like, must be placed either before, after, or between heat exchangers of such furnaces to assure a proper combustion draft by either drawing or forcing air through the combustion chamber.
Presently, the housings of existing induced draft blowers have been of sheet metal construction, spot welded to achieve the desired structure and configuration. Such units are difficult to mount on the furnace panels, and are not conductive to implemetation with sophisticated sensors to achieve safe and efficient operation. Because of the sheet metal fabrication of the prior housings, they are typically rectangular in nature, having a rectangular exhaust which necessarily requires an adapter to allow the exhaust to mate with the typical round flue pipe or the like.
The corrosive nature of flue gas condensates has had adverse affects on the sheet metal blower housings of the prior art, causing the same to deteriorate in short periods of time.
Previously known induced draft blowers have also typically been characterized by an exhaust conduit entering the cavity of the blower fan in such a manner as to generate an audible pulsating sound as each of the fan vanes of the blower fan traverses an aligned wall defined by the interconnection of the conduit with the cavity. Further, known induced draft blowers typically are incapable of separately venting the furnace pilot light, provide no integral means for sensing the development of an operational vacuum, and are incapable of determining when the flue of the system is dangerously restricted.